Agricultural balers typically comprise two main parts used in the formation of the bales: a pre-compression chamber and a baling chamber. Crop material is gathered and pushed into the pre-compression chamber, where a slice of crop material is formed. The pre-compression chamber is linked to the baling chamber in such a manner that the slice of crop material can periodically be transferred into the baling chamber. In the baling chamber, a plunger reciprocally moves, thereby pressing a square bale from subsequently fed slices.
The plunger movement is powered via a main shaft driven by a motor. The motor can be a part of the baler, or can be a part of e.g. the tractor connected to the baler via a power take-off (PTO). In practice, this reciprocal movement of the plunger is often considered the most dominant movement in the baler, dominant meaning that other movements are made relative to this movement of the plunger. The reason is that the plunger movement requires the highest force (highest relative to other forces needed for operating the baler). Of all movements in the baler, the movement of the plunger shows the highest inertia.
The pre-compression chamber is adapted for receiving gathered crop material. To this end, the pre-compression chamber shows an inlet. The pre-compression chamber furthermore shows an outlet towards the baling chamber. Between the inlet and the outlet, a channel is defined in which crop material can gather into a slice of crop material. The pre-compression chamber comprises a slice pushing mechanism provided for pushing a slice of crop material formed in the pre-compression chamber through the outlet of the pre-compression chamber into the baling chamber. The sliced crop material is typically pushed in a first segment of the baling chamber. The first segment is typically located directly behind the plunger (the plunger being in the withdrawn position). Thereby the slice of crop material is pushed in the baling chamber, after which the plunger can propel the crop material into the baling chamber, thereby pushing the most recently entered slice into the baling chamber, making it a part of the square bale.
The pre-compression chamber comprises, for the purpose of pushing the slice into the baling chamber, a slice pushing mechanism. Different types of slice pushing mechanisms are known, among which fingers grasping behind the slice and pushing the slice through the outlet, or a set of conveyer belts in between which the slice is formed, and which conveyer belts are driven to push the slice through the outlet.
The slice pushing mechanism is driven via a driving mechanism that is operationally linked to the plunger driving mechanism. A synchronized movement between the slice pushing mechanism and the plunger is needed to ensure a proper operation of the baler. Namely, only when the plunger is withdrawn, a slice can be pushed in the baling chamber. In practice, different synchronization types are possible among which a one/one synchronization, meaning that every withdrawal of the plunger a new slice is entered into the baling chamber, or a one/two synchronization, meaning that every other withdrawal of the plunger a new slice is entered, thus the plunger moves forth and back two times for each slice. Other synchronization timings, such as one/three, one/four, etc., are also possible.
Synchronization is in practice realized by mechanically linking the plunger driving mechanism and the slice pushing driving mechanism. Such mechanical link ensures proper synchronization, as the slice pushing mechanism is mechanically driven by the plunger movement, it cannot move out of synchronization.
A drawback relates to so-called top fill. Top fill is a measure for the uniformity of the slice after it has entered the first segment of the baling chamber. It will be recognized that a non-uniform fill, for example where the lower part of the first segment is more dense than an upper part, results in an inferior bale. Such top fill has an effect that a bale is highly dense at the lower end, and not dense at the top, resulting in an unstable bale that is likely to show a substantial deviation from the ideal square form. Such bale will bend like a banana resulting in a weirdly shaped bale. A negative top fill also results in a substantial wear of the plunger and baling chamber, as forces are not equally transmitted. The plunger will feel a substantially high resistance at the lower part of the plunger compared to the upper part resistance of the plunger. This will create a torque force exerted to the plunger which has to be borne by the plunger driving mechanism. When the ideal top fill can be obtained, a bale can be formed with nearly ideal outer dimensions and shape, and excessive wear on the baler mechanism can be avoided. In prior art balers, the ideal top fill is obtained by controlling the slice forming process in the pre-compression chamber. By obtaining a slice in which the crop material is evenly spread over the slice, after which the slice is pushed into the baling chamber, an acceptable top fill can be obtained.
A drawback of the existing top fill controlling mechanisms is that a deviation of the top fill can still occur depending on the baling speed and the type of crop material (hay, straw, silage, etc.).